Internet Protocol version 6 (IPv6) packet routing in logical and virtual network systems can be more challenging than packet routing in physical network appliances. The main challenges stem from the large number of logical routers that may be implemented in a logical network. Each of the logical routers uses a routing table to determine where packets received at the router should be transferred. The routing table for each logical router is stored in memory and, especially in cases where a large number of logical routers are implemented, large amounts of memory may be used to store the routing tables. Similarly, with a large number of routers to which packets may be transferred, performance of looking up routing information also becomes a factor.
Additionally, packet routing in logical networks does not necessarily follow the same constraints as packet routing in physical networks. For example, Tier0 logical routers comply with the address prefix length requirements of a physical network, since Tier0 routers bridge between logical and physical networks, and the prefix link is not controlled by a user. However, Tier1 logical routers route between logical networks of a data center. An administrator of that data center can therefore customize the network prefix lengths used by the subnets therein and the routing tables used by the logical routers would need to account for those customized prefixes.